[0001] The present invention generally relates to an optical coherence imaging device, and a method of forming an optical coherence imaging device.

[0002] Optical coherence imaging is well known in the art. During the last decades, optical coherence imaging has been increasingly used in the field of bio-imaging. For example, optical coherence imaging may be used for imaging a microstructure within a human body. In order to image a microstructure within a human body, the imaging device has to be introduced into the human body. However, when introducing the imaging device, sharp edges of the housing of the imaging device may harm the body or the microstructure to be imaged. In order to avoid such damages, circular or cylindrical housings may be used which do not include such sharp edges.

[0003] Optical coherence imaging devices as indicated above may comprise a light emitting arrangement configured to emit light onto a sample, a light receiving arrangement configured to receive light reflected by the sample, and a housing surrounding the light emitting arrangement and the light receiving arrangement, wherein the housing comprises a transparent element through which emitted light is directed onto the sample, and through which reflected light reflected by the sample is received by the light receiving arrangement.

[0004] Due to the circular or cylindrical shape of the housing, image quality may be negatively affected. That is, a cylindrical lensing effect of the transparent element may disturb the emitted light and the reflected light when passing through the transparent element.

[0005] Thus, there is a need to provide optical coherence imaging devices which avoid the above-mentioned problems. [0006] In order to solve the above objective, according to an embodiment of the present invention, an optical coherence imaging device is provided, comprising: a light emitting arrangement configured to emit light onto a sample; a light receiving arrangement configured to receive light reflected by the sample; and a housing surrounding the light emitting arrangement and the light receiving arrangement, wherein the housing comprises a transparent element through which emitted light is directed onto the sample, and through which reflected light reflected by the sample is received by the light receiving arrangement, wherein the transparent element comprises an outer housing surface having a cylindrical shape, and comprises an inner housing surface having a toriodal shape.

[0007] According to an embodiment of the present invention, at least a part of the housing has a tube-like cylindrical outer shape.

[0008] According to an embodiment of the present invention, at least a part of the transparent element has a ring-shaped form.

[0009] According to an embodiment of the present invention, the transparent element has a 360° ring-shaped form.

[0010] According to an embodiment of the present invention, the inner surface of the transparent element is coated by an antireflection coating.

[0011] According to an embodiment of the present invention, the antireflection coating transmits nearly 100 percent of light having a wavelength ranging from 800nm to 1500nm.

[0012] According to an embodiment of the present invention, the light emitting arrangement comprises a light reflecting element which reflects light propagating along a longitudinal axis of the housing towards the transparent element. [0013J According to an embodiment of the present invention, the light reflecting element is configured such that the light propagating along a longitudinal axis of the housing is reflected uniformly towards all areas of the ring-shaped surface element.

[0014] According to an embodiment of the present invention, the optical coherence imaging device further comprises a lens arrangement through which the light propagating along the longitudinal axis passes before reaching the reflective element.

[0015] According to an embodiment of the present invention, the optical coherence imaging device further comprises a numerical aperture changing means for changing a numerical aperture of the lens arrangement, wherein the numerical aperture changing means is operable such that the position of a focal point of the emitted light is shifted to a desired position by changing the a numerical aperture of the lens arrangement.

[0016] According to an embodiment of the present invention, the numerical aperture changing means is configured for changing a numerical aperture of the lens arrangement within a range between 0.04 and 0.1.

[0017] According to an embodiment of the present invention, the numerical aperture changing means is configured for changing a numerical aperture of the lens arrangement within a range between 0.04 and 0.08.

[0018] According to an embodiment of the present invention, the light reflecting element is configured such that the reflected light which propagates through the transparent element is reflected by the light reflecting element to propagate along the longitudinal axis of the housing in an opposite direction compared to the emitted light.

[0019] According to an embodiment of the present invention, the reflected light propagates through the lens arrangement. [0020] According to an embodiment of the present invention, reflected light is superimposed with emitted light in order to determine information about the sample.

[0021] According to an embodiment of the present invention, the emitted light /reflected light is infrared light.

[0022] According to an embodiment of the present invention, the wavelength of the emitted light ranges between 800nm to 1400 nm.

[0023] According to an embodiment of the present invention, the wavelength of the emitted light is about 1310 nm.

[0024] According to an embodiment of the present invention, the emitted light may be laser light.

[0025] According to an embodiment of the present invention, optical image device is an endoscopic device.

[0026] According to an embodiment of the present invention, the material of the housing of the optical image device comprises polycarbonate, polypropylene, stainless steel, glass, PDMS, PMMA or any other injection moldable/casting based transparent material, or any combination of these materials.

[0027] According to an embodiment of the present invention, the thickness of the housing of the optical image device or of the transparent element ranges between 0.05mm and 0.3mm.

[0028] According to an embodiment of the present invention, a diameter of the housing or a diameter of the transparent element ranges between 0.5mm to 5mm.

[0029] According to an embodiment of the present invention, the housing of the optical coherence imaging device is made of a bio-compatible material. "Bio-compatible" here means "compatible" for the purpose of in-vivo applications. That is, the material should not produce any toxic materials harmful to the body.

[0030] According to an embodiment of the present invention, a method of forming an optical coherence imaging device is provided, the method comprising: providing a light emitting arrangement configured to emit light onto a sample; providing a light receiving arrangement configured to receive light reflected by the sample; and providing a housing surrounding the light emitting arrangement and the light receiving arrangement, wherein the housing is formed such that it comprises a transparent element through which emitted light can be directed onto the sample, and through which reflected light reflected by the sample can be received by the light receiving arrangement, wherein the transparent element comprises an outer housing surface having a cylindrical shape, and comprises an inner housing surface having a toriodal shape.

[0031] According to an embodiment of the present invention, the housing is formed using the following processes: injection molding, casting, machining, or extrusion.

[0032] If an injection molding method is used, the housing may either be formed using a single mold, or a multiple mold. Multiple mode means in this context that the housing will not be formed by using a single mold. Different housing parts may be manufactured which are then joined together. So few molds will be used to fabricate different parts of the housing.

[0033] As will become apparent below, embodiments of the present invention may be applied to OCT (optical coherence tomography) bio-imaging which is a new emerging technique for higher resolution biopsies and other medical diagnostic applications as well. OCT imaging can achieve real time cellular scale resolution, which is important to produce high resolution cross-sectional images of the internal micro structure of living tissues. Higher resolution combined with real time mode makes the optical probe OCT imaging an important tool for accurate cancer diagnostics and monitoring to avoid recurring of cancer lesions. OCT based on miniaturized probes may be used where excision biopsy is unsafe or not possible. It can also be used in delicate interventional procedures, such as for neural investigations in brain and to reduce sampling errors due to the fact that it is real time.

[0034] The optical probe may be one of the critical elements in OCT imaging, as this makes the OCT imaging real time. The miniaturized optical probe helps in reducing patient's trauma by eliminating tissue removal required for biopsy. Since the miniaturized optical probe needs to be used inside the body, it may be enclosed in a biocompatible housing. The main requirement of the housing is it should be transparent to IR wavelength, especially at 13 lOnm. To minimize the effect of the sharp edges on the probe housing, cylindrical/circular shape may be used for enclosing the components. It is found that the circular shape of the housing with a wall thickness affects image quality because the cylindrical lensing effect diverges the light beam. The beam divergence/de focusing effect affects the image quality. To avoid the image distortion/aberration (also known as astigmatism), the cylindrical cross section of the probe may be modified to a toriodal shape. In a toriodal shape, the housing inner and outer diameter surfaces are curved which results in beam which is better focused into a single point.

[0035] Optical sensors may be widely used in bio applications because of their non-contact nature. One important optical application in biosystems is imaging. Various different optical imaging techniques are available, which are limited by depth of penetration and resolution. Optical coherence tomography (OCT) may be an imaging technique used to obtain high resolution cross-sectional images of micro structure in transparent and non transparent biological tissues. The OCT setup may be similar to a Michelson interferometer and may comprise a reference arm and an incident (scanning) arm. In the incident arm, the light falls onto the specimen, and the reflected light is captured and processed for imaging. A probe is necessary to focus the incident light onto the sample and to collect the reflected light. The optical probe may be a biosensor consisting of optical components, and a scanning component, and may be an integral part of the OCT system.

[0036] OCT systems may be used in ophthalmology and cardiology applications. One of the advantages of using OCT in imaging is the possibility of in-vivo imaging applications. In the conventional OCT setup, the probe used is large, and hence imaging by in-vivo technique is quite difficult. According to embodiments of the present invention, the probe may be used as an endoscope so that the internal tissue imaging can be performed. Morphological changes in the internal organ's tissue can be identified by changes in the images. Comparing an image of healthy tissue with the newly taken image can ascertain whether there is any abnormality in the organ.

[0037] Different types of OCT system may be used, for example a swept source OCT (SS OCT), where rapid scanning of narrow-band source spectra is performed, and a spectral domain OCT (SD OCT), wherein a Fourier domain detection technique may be used in these cases.

[0038] Miniaturized probes may be used in OCT systems for in situ in-vivo imaging application. Miniaturized probes with additional features may be used to get complete imaging without rotating the probe. The probes may be designed based on the type of application, either forward imaging or side imaging types. Forward imaging probes can provide tissue structural information such as image guided biopsy while the side imaging probes are suitable for imaging within a tubular organ such as gastrointestinal tract, urinary tract etc. [0039] According to an embodiment of the present invention, a 3D micro mirror may be used as a scanning to scan the beam onto the sample for imaging. In this optical biosensor probe, a laser beam having a wavelength of 1300nm may be used.

Brief Description of the Drawings

[0040] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which:

FIG. 1 shows a schematic cross-sectional drawing of an optical coherence imaging device according to an embodiment of the present invention;

FIG. 2 shows a schematic drawing of an optical coherence imaging device according to an embodiment of the present invention;

FIG. 3 shows schematic drawings of different focal points of optical coherence imaging devices according to an embodiment of the present invention;

FIG. 4 shows a schematic drawing of an optical coherence imaging device according to an embodiment of the present invention;

FIG. 5 shows schematic cross-sectional drawing of a part of an optical coherence imaging device according to an embodiment of the present invention;

FIG. 6 shows a diagram indicating different astigmatisms resulting when using optical coherence imaging devices having different housing dimensions;

FIG. 7 shows a beam profile of an emitted light beam of a conventional optical coherence imaging device; FIG. 8 shows a simulation of a cross-section of the light beam shown in FIG. 7;

FIG. 9 shows a beam profile of an emitted light beam of an optical coherence imaging device according to an embodiment of the present invention;

FIG. 10 shows a simulation of a cross-section of the light beam shown in FIG. 9;

FIG. 1 1 shows experimental results corresponding to the simulation of FIG. 8;

FIG. 12 shows experimental results corresponding to the simulation of FIG. 10;

FIG. 13 shows a part of a transparent element according to an embodiment of the present invention; and

FIG. 14 shows a schematic drawing of an optical coherence imaging device according to an embodiment of the present invention;

Description

[0041] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0042] Figure 1 shows a schematic cross-sectional drawing of an optical coherence imaging device 100 according to an embodiment of the present invention. The optical coherence imaging device 100 comprises: a light emitting arrangement 102 configured to emit light 104 onto a sample 106; a light receiving arrangement 108 configured to receive light 110 reflected by the sample 106; and a housing 112 surrounding the light emitting arrangement 102 and the light receiving arrangement 108, wherein the housing 112 comprises a transparent element 114 through which emitted light 104 is directed onto the sample 106, and through which reflected light 110 reflected by the sample 106 is received by the light receiving arrangement 108, wherein the transparent element 114 comprises an outer housing surface 116 having a cylindrical shape, and comprises an inner housing surface 118 having a toriodal (i.e. curved) shape.

[0043] According to an embodiment of the present invention, the optical coherence imaging device 100 shown in figure 1 is a probe, i.e. a device which can be introduced into a body of a human or of an animal. Alternatively, the optical coherence imaging device 100 shown in figure 1 may be a "stand alone device", i.e. a device not being suitable for being introduced into a body of a human/animal.

[0044] According to an embodiment of the present invention, the whole housing 112 may be transparent. Alternatively, only the transparent element 114 may be transparent.

[0045] According to an embodiment of the present invention, the material of the housing 1 12 may be glass or polycarbonate, polypropolyne, stainless steel, glass, PDMS

(polydimethylsiloxane), PMMA (polymethylmethacrylate), or any other injection

moldable/casting based transparent material, or any combination of these materials.

[0046] According to an embodiment of the present invention, the material of the transparent element 114 may be glass, polycarbonate, polypropolyne, glass, PDMS, PMMA, or any other injection moldable/casting based transparent material. The transparent element 114 may be made by a plurality of different layers. For example, the base material of the transparent element 114 may be any of the above indicated materials or combinations thereof, wherein the inner surface of the transparent element 114 (toriodal surface) may be covered by a further layer, for example an anti-reflective layer. [0047] In this embodiment, the light emitting arrangement 102 and the light receiving arrangement 108 are the same component, for example a mirror. However, the light emitting arrangement 102 and the light receiving arrangement 108 may also be different components.

[0048] According to an embodiment of the present invention, the light emitting arrangement 102 may generate the emitted light 104 itself. Alternatively, the light emitting arrangement 102 may only receive light already generated (by a different component of the optical coherence imaging device 100 (not shown)) and direct it as emitted light 104 onto the sample 106.

[0049] figure 2 shows a schematic drawing of an optical coherence imaging device 200 according to an embodiment of the present invention. The optical coherence imaging device 200 comprises a probe 250. The probe 250 comprises a light emitting arrangement 202 configured to emit light 204 onto a sample 206; a light receiving arrangement 208 configured to receive light 210 reflected by the sample 206; and a housing 212 surrounding the light emitting arrangement 202 and the light receiving arrangement 208, wherein the housing 212 comprises a transparent element 214 through which emitted light 204 is directed onto the sample 206, and through which reflected light 210 reflected by the sample 206 is received by the light receiving arrangement 208, wherein the transparent element 214 comprises an outer housing surface 216 having a cylindrical shape, and comprises an inner housing surface 218 having a toriodal shape.

[0050] In this embodiment, the light emitting arrangement 202 and the light receiving arrangement 208 are a common reflective element like a mirror (like a MEMS micro mirror) which may be aligned with regard to its relative position to the probe housing 212, thereby reflecting light 220 received from a lens arrangement 222 (e.g. a GRIN (Graded Index) lens arrangement) towards different areas of the sample 206 as emitted light 204, depending on the alignment of the reflective element. In the same way, light 210 reflected by the sample 206 may be received by the reflective element and reflected as light 224 towards the lens arrangement 222. In this embodiment, the reflective element (light emitting arrangement 202) may be supported by or integrated within a substrate 226.

[0051] In this embodiment, the alignment of the mirror may be changed (e.g. by a corresponding reflective element drive) such that the light 204 is successively directed onto the sample 206 in a 360° manner (or a part thereof). This means that an 360° image of the sample 206 can be obtained easily. Alternatively, the reflective element may be shaped such that an 360° image (or a part thereof) of the sample 206 can be obtained without changing the alignment of the reflective element.

[0052] According to an embodiment of the present invention, in alternative to the architecture of the probe 250 as shown in figure 2, the probe 250 may arranged such that the light 204 is directed through a tip portion 228 (front wall) of the housing 212 instead of directing the light 204 through the side walls of the housing 212. In this case, the reflective element 202 and the substrate 226 may be omitted, and the inner surface of the tip portion 228 of the housing 212 would be formed to be toriodal. In this case, however, the scanning area of the probe 250 would be limited, compared to the case shown in figure 2.

[0053] According to an embodiment of the present invention, the length of the probe ranges from 10mm to 30mm.

[0054] According to an embodiment of the present invention, a diameter (width) of the probe ranges from 0.5mm to 5mm.

[0055] According to an embodiment of the present invention, the length L of the probe 250 is about 25mm, whereas the width W of the probe 250 is about 2 to 3 mm [0056] According to an embodiment of the present invention, the optical coherence imaging device 200 works as follows: Light 260 is generated by a light source 262 and is guided through a circulator 264 to a beam junction 266. At the beam junction 266, a part of the light output by the circulator 264 is guided as scanning light 270 through the lens arrangement 222 to become light 220 which is reflected by the reflecting element (light emitting arrangement 202) onto the sample 206. The light 224 which is light reflected by the sample 206 is guided through the lens arrangement 222 and is guided as light 276 to the beam junction 266. A part of the light output by the circulator 264 is guided as reference light 268 through a collimator 272 to a reference mirror 274, where it is reflected and guided back to the beam junction 266. At the beam junction 266, the reflected reference light 268 is combined with light 276. Combined light 278 is then guided through the circulator 264 to the detector 280 which detects an interference between the reference light 268 and the scanning light 270. An output 282 of the detector 280 indicative of the surface structure of the sample 206 is then transferred to a signal processor 284 connected to a computer 286 which calculates the surface structure of the sample 206 based on the output signal 282 and provides a cross-sectional image of the sample 206.

[0057] Figure 3 shows the effect of using a transparent element 214 comprising an outer housing surface 216 having a cylindrical shape, and comprising an inner housing surface 218 having a toriodal shape. In figure 3, only a part of the transparent element 214 is shown.

[0058] In figure 3 a, the situation is shown where a light beam 300 is focused in a focal point 302 using a lens (GRIN lens) arrangement 222.

[0059] In figure 3b, the situation is shown where a light beam 300 is focused through a transparent element 214 having both a cylindrical outer surface and a cylindrical inner surface 218. In this way, no focal point as in figure 3a can be obtained since a focal point 304 of an x axis is different from a focal point 306 of a y axis. That is, because of the cylindrical lens effect of the housing 212, the x axis and the y axis of the optical beam 300 are not focused at a common point. This situation is comparable to the astigmatism found in human eyes where the x axis and the y axis are not focused.

[0060] The problem indicated in conjunction with figure 3b can be avoided if a transparent element 214 as shown in figure 3c is used. Compared to figure 3a, the transparent element 214 has a cylindrical outer surface and a toriodal inner surface 218. As a consequence, the light beam 300 can be focused again in a common focal point 308 for both x axis and y axis, as shown in figure 3 a. However, the focal point 308 is now quite far away from the transparent element 214.

[0061] The problem indicated in conjunction with figure 3c can be avoided if a numerical aperture of the lens arrangement 222 is changed. This decreases a distance between the focal point 310 and the transparent element 214. In other words: Because of the curvature of the housing 212, a working distance changes such that the diameter of the beam 300 increases at the focal point 302. This reduces the intensity at the focal point 302, see figure 3c. To bring back the working distance to the focal point 302, and to restore the original beam diameter, the NA of the lens arrangement 222 needs to be changed.

[0062] Figure 4 shows a detailed view of an embodiment of a housing of a probe as for example shown in figure 2. As can be derived from figure 4, the inner surface 218 of the transparent element 214 is a toriodal shaped surface, and the outer surface 216 of the transparent element 214 is a cylindrically shaped surface.

[0063] Figure 5 shows, similar to figure 4, how light 220 impinging on the reflective element 202 is reflected as emitted light through the side wall of the housing 212. In this embodiment, the thickness of the housing 212 is about 0.3 mm. [0064] Figure 6 shows a diagram indicating different astigmatisms resulting when using optical coherence imaging devices having different housing dimensions. That is, figure 6 shows that the samller the radius of a circular shaped housing of an optical coherence imaging device is, the larger the corresponding astigmatism is.

[0065] If figures 7 and 9 are compared, it can be derived that using a transparent element 214 having a toriodal shaped inner surface 218 (figure 9) enables to better focus a light beam 300 compared to the case where a cylindrical shaped inner surface 218 (figure 7) is used. In figure 7, the housing structure used is of a cylindrical shape, both inner and outer parts (218 and 212) are of a cylindrical shape, the beam 300 is not focused. But in the case of figure 9, the inner part 218 is of a toriodal shape while the outer part is of a cylindrical shape, and the beam 300 is focused.

[0066] Figure 8 shows a simulation of a cross-sectional view of the light beam 300 using the arrangement shown in figure 7. Similarly, figure 10 shows a simulation of a cross-sectional view of the light beam 300 using the arrangement shown in figure 9. As can be derived from a comparison between figures 8 and 10, the arrangement of figure 9 enables a much better focus of the light beam 300, compared to the case where the arrangement of figure 7 is used.

[0067] Figures 11 and 12 show the correlating experimental results of a focused light beam 300 (figure 11 shows a light beam obtained when using an arrangement as shown in figure 7, and figure 12 shows a light beam obtained when using an arrangement as shown in figure 9). As can be seen, the experimental results match the simulation results shown in figures 8 and 10. In this way, the simulation results shown in figures 8 and 10 are validated.

[0068] Figure 13 shows a segment of a ring-shaped transparent element 14 having a toriodal shaped inner surface 218 in the sense of embodiments of the present invention. As can be derived from figure 13, the transparent element 14 has an outer surface 216 which is flat, and an inner surface 218 which is curved. The inner surface 218 is curved in a sense that a thicknesses Tl of an upper part and a lower part of the transparent element 214 are larger than a thickness T2 of a middle part of the transparent element 214. The range of the ratio T1/T2 varies with application and requirements.

[0069] According to an embodiment of the present invention, a width W of the transparent element 214 ranges between 5mm to 30mm.

[0070] Figure 14 shows a schematic view of an optical coherence imaging device according to one embodiment of the present invention. In this embodiment, the reflecting element 202 reflects light 220 such that a maximum width 1400 of a surface area of the housing 212 is 20mm, i.e -10mm to +10mm from a mirror level 1402. Only this surface area needs to be transparent, the rest of the housing 212 does not need to be. More generally, a reflection angle a may range, depending on the rotation angle of the mirror (the rotation angle of the reflecting element 202), i.e. depending on the alignment of a reflecting surface of the mirror, between 10° and 90°. The reflection angle a is indicative of the maximum width 1400 of the surface area of the housing 212 onto which emitted light 204 impinges.

[0071] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.